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Abstract:

Abstract To advance our understanding of the causes and the consequences of budding (colony multiplication by fragmentation of main nests), we investigated nest movement in the facultatively polydomous Pharaoh ant, Monomorium pharaonis. Demographic data revealed that Pharaoh ants are highly polygynous and have a relatively low worker to queen ratio of 12.86. Budding experiments demonstrated that the number of available bud nests has a significant effect on colony fragmentation and increasing the number of bud nests resulted in smaller colony fragments. The overall distribution among bud nests was uneven, even though there was no evidence that the different life stages and castes partitioned unevenly among the bud nests and the analysis of individual colonies revealed no evidence of an uneven split in any of the colonies. This demonstrates that Pharaoh ants have the ability to exert social control over colony size and caste proportions during budding, which may contribute to their success as an invasive ant. The intensity of nest disturbance had a significant effect on whether or not the ants migrated into bud nests. Major disturbance resulted in the ants abandoning the source nest and migrating to bud nests and minor disturbance did not stimulate the ants to abandon the source nest. The results of the successive budding experiment which allowed the ants the opportunity to bud into progressively smaller nest fragments demonstrate that Pharaoh ants maintain a preferred minimum group size of 469 ± 28 individuals. Food allocation experiments utilizing protein marking revealed that nest fragmentation in Pharaoh ants has no negative impact on intracolony food distribution. Overall, our results suggest that nest units in the Pharaoh ant behave like cooperative, rather than competitive, entities. Such cooperation is most likely facilitated by the fact that individuals in all bud nests are genetically related, remain in close proximity to each other, and may continue to exchange individuals after budding.